Li-ion batteries (LIBs) remain the most prominent rechargeable, electrochemical energy storage technology [1], with tremendous importance for the portable electronics as well as for rapidly growing sector of environmentally-benign, electrical mobility [2]. A conceptually identical technology, Na-ion batteries (SIBs), is also emerging as a viable alternative due to much greater natural abundance and more even distribution of Na as compared to Li. The particularly strong appeals of commercialized LIBs are their long operation life span, over hundreds to thousands charge/discharge cycles, and superior and broadly tunable balance between the energy density and the power density [3]. This implies, inter alia, that in the search for alternative Li-ion anode materials not only reversible theoretical charge-storage capacities must be higher than that of Graphite (372 mAh g−1), but also satisfactory retention of capacity on a long-term and under fast charge/discharge cycling (high current densities) must be obtained. For instance, the transition from commercial graphite anodes to most intensely studied alternatives such as Si, Ge, Sn and some metal oxides, with 2-10 times higher theoretical capacities (with 3579 mAh g−1 for Si being the highest) [4] is primarily hampered by the structural instabilities caused by drastic volumetric changes up to 150-300% upon full lithiation to, e.g., Li3Sb, Li15Si9, Li15Ge4, Li22Sn5 [5] or by slow reaction kinetics. Presently, great research efforts are focusing on nanostructuring of the active material, by producing nanowires, nanoparticles and nanocrystals (NPs and NCs), in order to mitigate the effects of volumetric changes and to enhance the lithiation kinetics [6]-[13]. With regard to SIBs, it is important to note an even greater need for efficient anode materials, because silicon does not reversibly store Na-ions at ambient conditions [14], graphite shows negligible capacities of 30-35 mAh g−1 [15], while other carbonaceous materials exhibit capacities of less than 300 mAh g−1 at rather low current rates and suffer from the low tap density due to high porosity [12]. Contrary to LIBs, there is much greater progress for the Na-ion cathodes than for Na-ion anodes [16], [17].
In the elemental form, antimony (Sb) has long been considered as a promising anode material for high-energy density LIBs due to high theoretical capacity of 660 mAh g−1 upon full lithiation to Li3Sb [3], [4], and has gained a revived interest as mechanically-milled or chemically synthesized nanocomposites [18]-[21], as well as in form of bulk microcrystalline or thin-film material [22], [23]. Furthermore, stable and reversible electrochemical alloying of bulk Sb with Na has also been recently demonstrated [22], pointing to the utility of this element in SIBs as well. Several reports, published in 2012-2013, have demonstrated efficient Na-ion storage in Sb/C fibers [5], mechanically milled Sb/C nanocomposites [24], Sb/carbon nanotube nanocomposites [25] and in thin films [23].
Some documents disclose antimony based anode materials for a rechargeable Li-battery which comprise nanoparticles of SnSb (see Wachtler M. et al.: “Anodic materials for rechargeable Li-batteries”, Journal of Power Sources, Elsevier SA, CH; vol. 105, no 2, 20 Mar. 2002 (2002-03-20), pages 151-160; or Wachtler M. et al.: “Tin and tin-based intermetallics as new anode materials for lithium-ion cells”, Journal of Power Sources, Elsevier SA, CH; vol. 94, no 2, 1 Mar. 2001 (2001-03-01), pages 189-193) or which comprise nanoparticles of Sb (see Caballero et al.: A simple route to high performance nanometric metallic materials for Li-ion batteries involving the use of cellulose: The case of Sb″, Journal of Power Sources, Elsevier SA, CH; vol. 175, no 1, 26 Nov. 2007 (2007-11-26), pages 553-557 or Zhang et al.: “Lithium insertion/extraction mechanism in alloy anodes for lithium-ion batteries”, Journal of Power Sources, Elsevier SA, CH; vol. 196, no3, 1 Feb. 2011 (2011-02-01), pages 877-885). However, such nanoparticles are obtained by precipitation methods. Such precipitation methods are not able to produce monodisperse nanoparticles or nanocrystals.